Metal-insulator-metal tunnel junctions (MIMTJs) are fundamental building blocks for microelectronics including magnetic tunnel junctions (MTJs) for spintronics and fast access nonvolatile magnetic memory, and Josephson tunnel junctions (JJs) for particle detectors, magnetic field sensors, and qubits for quantum computation. The performance of MIMTJs depends critically on the quality of the insulating tunnel barrier. (L. A. Abelson et al., Proceedings of the IEEE, vol. 92, pp. 1517-1533, 2004.) Considering native oxides can naturally form on the surface of most metals, producing an atomically-thin, uniform, and pinhole-free tunnel barrier represents a major challenge in the research of MIMTJs. In Nb/Al/AlOx/Nb JJs, for example, an ultrathin tunnel barrier is the key to preserve phase coherence across the superconducting Nb electrodes, since the critical current (Ic) through the JJ exponentially decays with the barrier thickness. (A. W. Kleinsasser et al., Applied Superconductivity, IEEE Transactions on, vol. 5, pp. 26-30, 1995.) Thermal oxidation has been the industry standard to produce AlOx tunnel barriers for JJs through in situ oxygen diffusion into an Al wetting layer, however this diffusion mediated process has difficulty achieving a uniform tunnel barrier with a well-defined thickness. (B. Seeber, Handbook of applied superconductivity vol. 2: CRC press, 1998.) Despite successful commercial applications of these JJs in devices such as superconducting quantum interference devices (SQUIDs) and voltage standards, two-level defects (TLDs) in the AlOx tunnel barrier are one of the major sources of decoherence in superconducting qubits. (R. McDermott, Applied Superconductivity, IEEE Transactions on, vol. 19, pp. 2-13, 2009.)